By “rarest”, I mean the least used. Excluding archaic verbs, what verb has the least use?
My guess would be “twiddle”…it doesn’t seem to get much use these days.
This list claims to be the least common English words.
(alphabetical order)
I’d probably say ‘bing’ (to look something up online).
That’s nonsense. I know every one of those words, and some of them are used with great frequency, such as “renovation,” “hypothesis,” and “lobbyist.”
The phrase “twiddling his/her/their thumbs” is in common use though.
That list consists largely of quite common words such as “compassion”, “asylum” and “abstain”.
You can check the British National Corpus to give one measure of the relative frequency of various words. For example “twiddle” appears 23 times, so if you find verbs that score lower than that, you may consider them as candidates. Examples: “chide” (13), “derogate” (17). You can also refine the search to exclude academic text, include only spoken word, etc.
Questions like this are never meaningful, because it depends entirely on where you draw the “archaic” line. In principle, someone could make a big, long list of all English words in order of frequency of use. The top portion of the list is current, and the bottom portion is archaic, and so somewhere in between there has to be a transition from one to the other. Where do you want to draw that bright line that represents something that’s inherently fuzzy? I dunno, but wherever you draw it, there’s your answer.
There is neither a verb nor particularly rare in usage, so I really doubt it. 
Methinks Chronos hath given unto us a list wherethrough we shall peradventure win teh internets. Thou wist that I have spoken somedeal soothly.
Whatever it is, it’s likely you never heard of it. There’s an awful lot of extremely obscure words you can find in a large dictionary, that probably don’t count as archaic, but are so incredibly seldom used that practically nobody is familiar with the word. Often they are words used only in some very specialized field, like a specific word for weaning a yak calf from its mother, or something like this. In fact, there’s a parlor game based on words like these, which is currently being done on the NPR show “Says You” as their so called “bluffing round”. In their version of it, the moderator announces a horribly obscure word, and pieces of paper are handed to the three members of one team. One of them has the actual definition, the other two are to make up definitions within 30 seconds. They all read out their definitions, which are usually ALL extremely silly sounding, and the other team has to guess which one is the real definition.
Good point. A lot of people can probably come up with a few terms that have a restricted usage, even though many people probably can understand them. When was the last time since high school or college lab classes when you felt it important that something be deoxygenated or that some numerical measurements be metrificated?
Well, “wat” must be among the rarest pronouns, that’s for sure.
The effect is funnier when the word is not some technical jargon construct, and actually describes something strange to begin with. For instance, I just poked around and found one of their words was “catillate”, which means to lick dishes.
You mean like a cat?
We could never figure out in our French verb book what the verb “To gird on” meant. It was only later when listening to The Minstrel Boy that I figured it out.
I’m not sure the question can be answered. The BNC is way too small to get lots of really obscure words and all the different meanings and usages of all the words both common and obscure… Even if it were 1000 times larger than it is, it probably still would be inadequate.
For example, the word taco shows up 28 times in that corpus. How many times was it used as a verb? Looking at the 28 contexts, none at all. Yet it’s used as a verb in certain contexts (for instance you can taco your bicycle wheel. Where I work, we have a totally different use of taco as a verb.).
Another example, in his novel Even Cowgirls Get the Blues, Tim Robbins used science fiction as a verb. That’s pretty rare, I’d say, although I doubt if it’s anything close to the rarest.
That suggests itself, but it’s apparently rooted in Latin:
Which leaves us with the question of why the Romans felt they had to have a specific word to mean licking plates.
Correction. It was Still Life with Woodpecker and Tom Robbins, not Tim.
I am going to submit “girt” which is almost never used except in the Australian national anthem. 
Funny; I wouldn’t have considered “derogate” such an obscure word. It’s used relatively frequently in legal writing - a provision derogates from another. Maybe a term of art that is not used a lot in everyday writing, but I still would have thought that the legal usage alone would suffice to prevent it from being a fringe word.